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Oh yes I know you were referring to the wheel's rotational inertia, but as much of a knee-slapper that my answer wasn't, it's probably more important than the wheel's RI.
But, to answer your question: if you assume that a wheel is a solid disk (which of course it's not, but close enough) you can calculate its moment of inertia as I = (mass • radius^2)/2.
So, for two 16" wheels, one 15 lbs and one 25 lbs, you'll get a net gain of 1280 inch-squared-pounds, per wheel, by reducing the mass of the wheel. This really only matters on the driven wheels.
But since the moment of inertia of a rotating disk is a function of the radius squared, you'll get a bigger bang for your buck by reducing the wheel's radius than it's mass. Better, do both.
Now, reducing the wheel's radius will usually increase the tire's profile, increasing the amount of rubber that has to deform every time the wheel turns, decreasing rolling resistance, etc. This is probably a negligible offset, however.
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2004 Matrix Base • FWD • 1zz-FE • Manual • Gislaved Nordftost 5 (NS) 205 55 16
Up-to-date info about my car is here.
Last edited by msanford; 10-23-2008 at 08:53 PM.
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